The presently disclosed embodiments relate generally to the formulation of a layer that provides overall flatness to imaging apparatus flexible members and components for use in electrostatographic, including digital, apparatuses. More particularly, the embodiments pertain to a flexible electrophotographic imaging member belt prepared to include an anticurl back coating formulated to comprise a dispersion of conductive carbon nanotubes in a specific polymer blend. The polymer blend comprises an anti-static polymer, a bisphenol polycarbonate, and low surface energy polycarbonate to: (a) render electrical conductivity effect for tribo-electrical charge elimination (b) impart static dissipation capability, and (c) provide surface energy lowering effect for contact friction reduction to ease imaging member belt drive as well as cutting tribo-electrical charge build-up under normal imaging member belt operational conditions in the field.
Flexible electrostatographic imaging members are well known in the art. Typical flexible electrostatographic imaging members include, for example: (1) electrophotographic imaging member belts (photoreceptors) commonly utilized in electrophotographic (xerographic) processing systems; (2) electroreceptors such as ionographic imaging member belts for electrographic imaging systems; and (3) intermediate toner image transfer members such as an intermediate toner image transferring belt which is used to remove the toner images from a photoreceptor surface and then transfer the very images onto a receiving paper. The flexible electrostatographic imaging members may be seamless or seamed belts. A seamed belt is usually formed by cutting a rectangular imaging member sheet from a web stock, overlapping a pair of opposite ends, and welding the overlapped ends together to form a welded seam belt. Typical electrophotographic imaging member belts, include a charge transport layer and a charge generating layer on one side of a supporting substrate layer, but exhibit undesirable upward curling, so an anti-curl back coating is coated onto the opposite side of the substrate layer to render imaging member belts flatness. A typical electrographic imaging member belt does, however, have a more simple material structure. Although it includes only a dielectric imaging layer on one side of a supporting substrate, an anti-curl back coating is still needed on the opposite side of the substrate for curl control. Although the scope of the present embodiments cover the preparation of all types of flexible electrostatographic imaging members, for simplicity, the discussion hereinafter will be focused on and represented only by flexible electrophotographic imaging members.
Flexible electrophotographic imaging members include a photoconductive layer having a single layer or composite layers. Because typical electrophotographic imaging members exhibit undesirable upward imaging member curling, an anti-curl back coating is required to offset the curl. Thus, the application of the anti-curl back coating is used to render the imaging member with appropriate flatness.
Electrophotographic imaging members, e.g., photoreceptors, photoconductors, and the like, include a photoconductive layer formed on an electrically conductive substrate. The photoconductive layer is an insulator in the substantial absence of light so that electric charges are retained on its surface. Upon exposure to light, charge is generated by the photoactive pigment, and under applied field charge moves through the photoreceptor and the charge is dissipated.
In electrophotography, also known as xerography, electrophotographic imaging or electrostatographic imaging, the surface of an electrophotographic plate, drum, belt or the like (imaging member or photoreceptor) containing a photoconductive insulating layer on a conductive layer is first uniformly electrostatically charged. The imaging member is then exposed to a pattern of activating electromagnetic radiation, such as light. Charge generated by the photoactive pigment moves under the force of the applied field. The movement of the charge through the photoreceptor selectively dissipates the charge on the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image. This electrostatic latent image may then be developed to form a visible image by depositing oppositely charged particles on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the imaging member directly or indirectly (such as by a transfer or other member) to a print substrate, such as transparency or paper. The imaging process may be repeated many times with reusable imaging members.
Multilayered photoreceptors or imaging members have at least two layers, and may include a substrate, a conductive layer, an optional undercoat layer (sometimes referred to as a “charge blocking layer” or “hole blocking layer”), an optional adhesive layer, a photogenerating layer (sometimes referred to as a “charge generation layer,” “charge generating layer,” or “charge generator layer”), a charge transport layer, and an optional overcoating layer in either a flexible belt form or a rigid drum configuration. In the multilayer configuration, the active layers of the photoreceptor are the charge generation layer (CGL) and the charge transport layer (CTL). Enhancement of charge transport across these layers provides better photoreceptor performance. Multilayered flexible photoreceptor members may include an anti-curl back coating (ACBC) layer on the backside of the substrate, opposite to the side of the electrically active layers, to render the desired photoreceptor flatness.
In current organic belt photoreceptors, an anti-curl back coating layer is used to balance residual stresses caused by the top CTL coating of the photoreceptor and eliminate curling. In addition, the ACBC layer should have optically suitable transmittance, for example, transparent, so that the photoreceptor can be erased from the back. Existing formulations for anti-curl back coating layers are of low conductivity such that the anti-curl back coating layer takes on a tribo-electrical charge during use in the image-forming apparatus. This tribo-electrical charge increases drag in the image-forming apparatus and increases the load on the motor and wear of the anti-curl back coating layer. Additional components, such as active countercharge devices, or additives, such as conductive agents, have been used to attempt to eliminate the tribo-charging of the layer. However, these options are not desirable as they increase costs and complexity by including additional components or include additives which produce ACBC dispersions that do not have the suitably optical clarity to allow imaging member back erase. Thus, there is a need for an improved ACBC that does not suffer from the above-described problems.
Relevant prior arts to the present disclosure are collectively summarized for reference and presented in the following:
U.S. patent application Ser. No. 12/851,193 to Yu et al., discloses an electrostatographic imaging member comprising an anticurl back coating layer formulated to comprise a polymer blend of an anti-static polymer and a low surface energy A-B diblock copolymer polymer and an adhesion promoter. The embodiments provide an imaging member belt with the anticurl back coating that is electrically conductive and also substantially reduces its surface contact friction to help suppress/eliminate tribo-electrical charge build-up at the backside of the imaging member belt under normal machine imaging member belt operational conditions in the field.
U.S. Pat. No. 5,919,590 discloses an electrostatographic imaging member comprising a supporting substrate having an electrically conductive layer, at least one imaging layer, an anti-curl layer, an optional ground strip layer and an optional overcoat layer, the anti-curl layer including a film-forming polycarbonate binder, an optional adhesion promoter, and optional dispersed particles selected from the group consisting of inorganic particles, organic particles, and mixtures thereof.
In U.S. Pat. No. 5,069,993, an exposed layer in an electrophotographic imaging member is provided with increase resistance to stress cracking and reduced coefficient of surface friction, without adverse effects on optical clarity and electrical performance. The layer contains a polymethylsiloxane copolymer and an inactive film-forming resin binder. Various specific film-forming resins for the anti-curl layer and adhesion promoters are disclosed.
U.S. Pat. No. 5,021,309 discloses an electrophotographic imaging device, with material for an exposed anti-curl layer has organic fillers dispersed therein. The fillers provide coefficient of surface contact friction reduction, increased wear resistance, and improved adhesion of the anticurl layer, without adversely affecting the optical and mechanical properties of the imaging member.
In U.S. Pat. No. 4,654,284 an electrophotographic imaging member is disclosed comprising a flexible support substrate layer having an anticurl layer, the anti-curl layer comprising a film-forming binder, crystalline particles dispersed in the film-forming binder and a reaction product of a bifunctional chemical coupling agent with both the binder and the crystalline particles. The use of VITEL PE 100 in the anticurl layer is described.
The above prior art disclosures demonstrate that, while attempts to resolve ACBC layer failures described above have been successful with providing some solutions, often times such solutions generate another set of problems. Therefore, there is a need to provide improved imaging members that have mechanically robust outer layers to effect service life extension but without causing the introduction of other undesirable problems.